Method and apparatus for use in selectively fracing a well

ABSTRACT

An apparatus for selectively fracing a well includes a tubular body having an exterior surface, and an interior surface that defines an interior bore. An annular flow area that has at least one fluid flow port extends radially through the tubular body to permit fluids from the interior bore to pass through the at least one fluid flow port into a surrounding earth formation. An external sealing sleeve selectively covers the annular flow area. There is a pressure actuated sleeve shifting mechanism, where increasing pressure tending to cause axial movement of the external sealing sleeve. The axial movement is resisted until a pre-selected pressure threshold is reached to permit movement of the external sealing sleeve to open the at least one fluid flow port.

FIELD

There is disclosed a method and apparatus for placing multiple fracturesat spaced locations along a well bore.

BACKGROUND

U.S. Pat. No. 7,267,172 (Hofman) entitled “Cemented Open Hole SelectiveFracing System” teaches selectively opening holes in production tubingof a hydrocarbon producing well by using sliding valves which can beselectively opened by a shifting tool. U.S. Pat. No. 7,096,954 (Weng etal.) entitled “Method and Apparatus for Placement of Multiple Fracturesin Open Hole Wells” teaches using a plurality of burst disk assemblies,each having an independent burst pressure. The present method providesan alternative method of selectively opening holes in production tubing.

SUMMARY

There is provided an apparatus for use in selectively fracing a well.The apparatus comprises a tubular body having an exterior surface, andan interior surface that defines an interior bore. An annular flow areathat has at least one fluid flow port extends radially through thetubular body from the interior surface to the exterior surface to permitfluids from the interior bore to pass through the at least one fluidflow port into a surrounding earth formation. An external sealing sleeveis detachably secured to the exterior surface of the tubular body toselectively cover the annular flow area and close the at least one fluidflow port. There is a pressure actuated sleeve shifting mechanism, withincreasing pressure tending to cause axial movement of the externalsealing sleeve. Axial movement is resisted until a pre-selected pressurethreshold is reached to permit movement of the external sealing sleeveto open the at least one fluid flow port.

There is also provided a method for use in selectively fracing a wellcomprising the following steps: (a) providing a plurality of apparatusas described above; (b) deploying the apparatuses along a productiontubing string in a well with packers being positioned between theapparatuses to isolate production areas, the pre-selected pressurethreshold for each production area increasing from a toe of the welltoward a heel of the well; (c) pumping fluids down the production tubingat pressures just sufficient to selectively shift the external sealingsleeve of the apparatus having a lowest shifting pressure to an openposition without shifting the external sealing sleeve of others of theapparatus having higher shifting pressures; (d) continuing to pumpfluids down the production tubing to pump fluids into the earthformation through the apparatus that has had its external sealing sleevemoved to the open position; (e) pumping balls down the production tubinguntil the balls seat on and close the at least one fluid flow port onthe apparatus that has had its external sealing sleeve moved to the openposition; (f) using fluid pressure to maintain the balls seated on theat least one fluid flow port while other of the external sealing sleevesin the production tubing are selectively moved to the open position; and(g) repeating steps (c), (d), (e) and (f) to selectively open theexternal sealing sleeve in apparatus in the production tubing in stages.

There is also provided an isolation tool for selectively applyingpressure to an outer tubular body. The isolation tool comprises atubular body carrying a first sealing element and a second sealingelement. The tubular body has a fluid inlet and a fluid outlet. Thetubular body is movable within the outer tubular body. A pressure cavityis defined by an outer surface of the tubular body, an inner surface ofthe outer tubular body, and the first and second sealing elements. Thefluid outlet of the tubular body is in fluid communication with thepressure cavity. The first sealing element and the second sealingelement permit fluid flow into the pressure cavity and sealing againstfluid flow out of the pressure cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features will become more apparent from the followingdescription in which reference is made to the appended drawings, thedrawings are for the purpose of illustration only and are not intendedto be in any way limiting, wherein:

FIG. 1 is a side elevation view in section of an apparatus forselectively fracing a well.

FIG. 2 is an end elevation view in section of a sealing sleeve of theapparatus depicted in FIG. 1.

FIG. 3 is a detailed side elevation view of the sealing cavity of thefluid cavity of FIG. 1.

FIG. 4 is a side elevation view in section of the sealing sleeve in theopen position.

FIG. 5 is a side elevation view in section of the flow ports pluggedwith balls.

FIG. 6 is a side elevation view of the apparatus depicted in FIG. 1installed in a tubing string and inserted into a well.

FIG. 7 is a side elevation view in section of an alternative tubularbody.

FIG. 8 is a side elevation view in partial section of an isolation tool.

FIG. 9 is a side elevation view in partial section of the isolation tooladjacent to the apparatus depicted in FIG. 1.

FIG. 10 is a side elevation view in section of an alternative apparatus.

DETAILED DESCRIPTION

An apparatus for use in selectively fracing a well generally identifiedby reference numeral 10, will now be described with reference to FIG. 1through 4. The use and operation of the apparatus will then be discussedwith reference to FIG. 1 through 6, 8 and 9. An alternative tubular bodywill be described with reference to FIGS. 7 and 10.

Structure and Relationship of Parts:

Referring to FIG. 1, apparatus 10 includes a tubular body 12 that has anexterior surface 14 and an interior bore 16 defined by an interiorsurface 17. An annular flow area 18 has one or more fluid flow ports 20extending radially through tubular body 12 from interior surface 17 toexterior surface 14. In FIG. 1, three flow ports 20 are included and inFIG. 2, the sealing sleeve 24 is designed to cover three. It will beunderstood that the number may be varied during construction ofapparatus 10, according to the preferences of the user or manufacturer.Fluid flow ports 20 permit fluids from interior bore 16 to pass throughfluid flow ports 20 into a surrounding earth formation.

Referring to FIGS. 1 and 2, an external sealing sleeve 24 is detachablysecured to exterior surface 14 of tubular body 12 to selectively coverannular flow area 18 and close fluid flow ports 20. External sleeve 24has a first end 26 with a first internal diameter that engages a firstsealing area 28 on exterior surface 14 of tubular body 12 on a firstside 30 of annular flow area 18. External sleeve has a second end 32with a second internal diameter that engages a second sealing area 34 onexterior surface 14 of tubular body 12 on a second side 36 of annularflow area 18. In the depicted embodiment, first sealing area 28 andsecond sealing area 34 have first and second seal grooves 38 and 40 inwhich are positioned first and second O-ring seals 42 and 44,respectively. A locking engagement is preferably provided betweenexternal sealing sleeve 24 and exterior surface 14 of tubular body 12 tolock external sealing sleeve 24 in the open position as shown in FIG. 4.For example, as depicted in FIG. 3, several resilient fingers 52 may becarried by external sealing sleeve 24. Resilient fingers 52 would thenengage an engagement profile 54 on exterior surface 14 of tubular body12 to maintain external sealing sleeve 24 in the open position.

Preferably, external sealing sleeve 24 is detachably secured to exteriorsurface 14 of tubular body 12 by shear pins 46 in shear pin apertures47. Exterior surface 14 of tubular body 12 has a circumferential shearpin groove 48 to accommodate shear pins 46. Shear pins 46 are designedto shear and permit external sealing sleeve 24 to move as pressurebuilds within annular flow area 18 and reaches a predetermined pressurethreshold. In a preferred embodiment, the number of shear pins 46 isadjustable, which permits a user to select a pre-selected pressurethreshold at which the external sealing sleeve 24 is able to move byusing a greater number or fewer number of shear pins 46.

External sealing sleeve 24 is moved by applying pressure to a pressureactuated sleeve shifting mechanism. For example, as shown in FIG. 3,external sealing sleeve 24 is shifted by applying pressure within afluid cavity 50 that is formed between external sealing sleeve 24 andexterior surface 14 of tubular body 12. Fluid cavity 50 is asymmetricalto provide an asymmetrical pressure distribution, so that increasingpressure within fluid cavity 50 tends to cause axial movement ofexternal sealing sleeve 24. In another example shown in FIG. 9, externalsealing sleeve 24 may also be shifted by applying pressure to aninclined plane 51 located at the end of fluid flow port 20. As pressurebuilds within this fluid flow port extension 50, pressure acts againsttapered wall 51 and pushes sealing sleeve 24 axially along apparatus 10.In either example, axial movement is resisted until a pre-selectedpressure threshold is reached, such as by using shear pins 46 asdescribed above. Once the pre-selected pressure threshold is reached,movement of external sealing sleeve 24 is permitted to open fluid flowports 20.

It will be understood that other pressure actuated sleeve shiftingmechanisms may be used, including different release mechanisms. Forexample, sleeve 24 may be biased to the shifted, open position, and apressure increase may release a catch that allows sleeve 24 to shift.

Operation:

Referring to FIG. 6, apparatuses 10 are deployed along a productiontubing string 53 with packers 55, such as hydraulically set dual elementopen hole packers. The type of packer used will be selected based on theconditions and preferences of the user. As apparatuses 10 are intendedto be used downhole, they may be hard coated with carbide seats toimprove durability. Referring to FIG. 1, each apparatus 10 is preparedby positioning external sealing sleeve 24 over annular flow area 18 suchthat flow ports 20 are blocked. External sealing sleeve 24 is thenlocked into the closed position by inserting a certain number of shearpins 46 that engage shear pin groove 48. The number of shear pins 46sets the pressure at which external sealing sleeve 24 will move, suchthat, by increasing the number of shear pins 46, the pre-determinedpressure also increases. Referring again to FIG. 6, packers 55 arepositioned between apparatuses 10 to isolate the desired productionareas. Tubing string 53 is then inserted into the casing 56 of awellbore 58, in this case, a horizontal wellbore, such that eachapparatus 10 is aligned with the portion of the formation to be fraced.

Once tubing string 53 is positioned with packers 55 set, fluids arepumped down tubing string 53 at pressures just sufficient to selectivelyshift external sealing sleeve 24 of apparatus 10 having the lowestpre-determined shifting pressure to an open position as shown in FIG. 3,such that fingers 52 engage profile 54, without shifting other externalsealing sleeves 24 that have higher shifting pressures. Fluids arecontinued to be pumped down production tubing 53 to pump fluids into theearth formation through apparatus 10 that has had its external sealingsleeve 24 moved to the open position to treat the formation. Oncetreated, balls 60 are then pumped down tubing 53 until balls 60 seat on,and close fluid flow ports 20 on the open apparatus 10 as shown in FIG.5. Fluid pressure is maintained to keep balls 60 seated on fluid flowports 20. Fluid pressure is then increased until the next pre-determinedpressure threshold is met to move the desired external sealing sleeve 24to the open position. These steps are repeated to selectively open thedesired external sealing sleeves 24 in the desired order, generally bystarting toward the toe 62 and working toward the heel 64 if the well isa horizontal wellbore, or from the end of the wellbore and workingbackward.

The operation steps above are based on using differential pressures toopen selected sealing sleeves 24. It has been found that in somecircumstances, the flow ports 20 closest to the wellhead may becomewashed out by the abrasives, and become unusable. It will be understoodother methods may also be employed, and may be preferable in somecircumstances. For example, referring to FIG. 8, an isolation tool 70may be used to apply pressure to a specific portion of tubing string 53shown in FIG. 6. Isolation tool 70 may be a cup frac tool, which is usedto selectively frac a portion of a formation. Isolation tool 70 has aninput 72 in fluid communication with an output or fluid flow ports 74,with sealing elements 76 positioned on either side of fluid flow ports74. Input 72 is connected to another tubing string (not shown) thatextends to the surface, such that fluid pressure may be applied bypumping fluid through the tubing string and out outputs 74, as shown byarrows 78. Isolation tool 70 is inserted into tubing string 53 untilfluid flow ports 20 of a selected apparatus 10 are positioned betweensealing elements 76. Referring to FIG. 9, sealing elements 76 engageinterior surface 17 such that the fluid pressure is applied to theselected fluid flow ports 20. Once the fluid pressure causes externalsealing sleeve 24 to shift as described above, pressure is continued tobe applied to frac the portion of the formation corresponding to thoseports 20. This method negates the need for providing increasing openingpressures for each apparatus 10, as well as the need to pump balls downtubing string 53 to plug the opened fluid flow ports 20. It also reducesthe risk of ports 20 becoming prematurely washed out. Once the frac iscomplete for that section, isolation tool 70 is repositioned at the nextset of fluid flow ports, and the process is repeated. This also leaves afull bore access as the internal components used to shift sleeve 24 areremoved.

Isolation tool

In the example described above, an isolation tool 70 is used to applypressure to a specific portion of outer tubular member, or tubing string53. It will be understood that this particular tool may be used forother tools aside from a sealing sleeve 24. For example, the isolatedpressure may be used to open various types of pressure-actuatedopenings, such as rupture discs, removable plugs, shifting sleeves, etc.as are known in the art.

Referring to FIG. 8, isolation tool 70 has sealing elements 76 that arein constant contact with the inner surface of an outer tubular body,such as tubing string 53, during installation. To prevent a fluid block,isolation tool 70 has an equalization valve 86 that is open when tool 70is being run in, and closes when pressure is applied within the pressurecavity 88 that is defined by sealing elements 76, the outer surface oftubular member 12, and As sealing elements 76 are cup-shaped, theypermit fluid to flow past in one direction, but create a seal when aforce is applied in the other directions. Thus, as tool 70 is being runin, fluid flows past the lower sealing element 76 and throughequalization valve 86. As tool 70 is being pulled out, fluid above tool70 passes over the upper sealing element 76 and through equalizationvalve 86. Equalization valve 86 is preferably adjustable such that thepressure at which it closes is adjustable. Once positioned, fluidpressure is applied between sealing elements 76 and as pressure buildswithin pressure cavity 88, sealing elements 76 are sealed against theinner surface of outer tubular body 53. Preferably, sealing elements 76are biased into sealing contact with tubular body 53, otherwise thepressurized fluid may flow around elements 76 and out of pressure cavity88.

Variations

FIG. 7 shows a slightly modified tubular body 12. Compared with FIG. 1,tubular body 12 has been lengthened. This has the effect of lockingexternal sealing sleeve 24 (not shown) further from flow ports 20. Inaddition, instead of a shoulder that is engaged, profile 54 is a groove.This allows tubular body 12 to have a thicker sidewall past profile 54.Finally, tubular body has a slightly angled surface 66 between sealgroove 40 and shear pin groove 48. While not shown, external sealingsleeve 24 will also have a corresponding angled surface 66.

FIG. 10 shows another modification, where, instead of finger 52 engagingshoulder 54, a ratcheting system is provided, where a profiled element80 engages a profiled surface 82 on tubular body 12. The top surface ofelement 80 is sloped and engages a sloped surface within externalsealing sleeve 24, such that any reverse movement is discouraged by theengagement between element 80 and surface 82, which increases due to thesloped surfaced as any reverse force increases. Preferably, element 80is enclosed within a resilient portion of sleeve 24, such as a splitring-type design, such that sleeve 24 is able to flex, but still appliespressure to element 80. Also shown in FIG. 10 is an inner sleeve 84 thatcan be shifted back to close off ports 20 if desired.

In this patent document, the word “comprising” is used in itsnon-limiting sense to mean that items following the word are included,but items not specifically mentioned are not excluded. A reference to anelement by the indefinite article “a” does not exclude the possibilitythat more than one of the element is present, unless the context clearlyrequires that there be one and only one of the elements.

The following claims are to be understood to include what isspecifically illustrated and described above, what is conceptuallyequivalent, and what can be obviously substituted. Those skilled in theart will appreciate that various adaptations and modifications of thedescribed embodiments can be configured without departing from the scopeof the claims. The illustrated embodiments have been set forth only asexamples and should not be taken as limiting the invention. It is to beunderstood that, within the scope of the following claims, the inventionmay be practiced other than as specifically illustrated and described.

1. An apparatus for use in selectively fracing a well, comprising: atubular body having an exterior surface, and an interior surface thatdefines an interior bore; an annular flow area having at least one fluidflow port extending radially through the tubular body from the interiorsurface to the exterior surface to permit fluids from the interior boreto pass through the at least one fluid flow port into a surroundingearth formation; an external sealing sleeve detachably secured to theexterior surface of the tubular body to selectively cover the annularflow area and close the at least one fluid flow port; a pressureactuated sleeve shifting mechanism, where increasing pressure tending tocause axial movement of the external sealing sleeve, such axial movementbeing resisted until a pre-selected pressure threshold is reached topermit movement of the external sealing sleeve to open the at least onefluid flow port.
 2. The apparatus of claim 1, wherein the pressureactuated sleeve shifting mechanism is a fluid cavity formed between theexternal sealing sleeve and the exterior surface of the tubular body,the fluid cavity being asymmetrical to provide an asymmetrical pressuredistribution so that increasing pressure within the fluid cavity tendsto cause axial movement of the external sealing sleeve.
 3. The apparatusof claim 1, wherein the pressure actuated sleeve shifting mechanism isan inclined plane in fluid pressure communication with at least onefluid flow port.
 4. The apparatus of claim 1, wherein the externalsleeve has a first end with a first internal diameter that engages afirst sealing area on the exterior surface of the tubular body on afirst side of the annular flow area and the external sleeve has a secondend with a second internal diameter that engages a second sealing areaon the exterior surface of the tubular body on a second side of theannular flow area.
 5. The apparatus of claim 4, wherein the firstsealing area has a first seal groove in which is positioned a firstO-ring seal and the second sealing area has a second seal groove inwhich is positioned a second O-ring seal.
 6. The apparatus of claim 1,wherein a locking engagement is provided between the external sealingsleeve and the exterior surface of the tubular body to lock the externalsealing sleeve in the open position.
 7. The apparatus of claim 6,wherein several resilient fingers are carried by the external sealingsleeve and the exterior surface of the tubular body has an engagementprofile that the resilient fingers engage to maintain the externalsealing sleeve in the open position.
 8. The apparatus of claim 1,wherein the external sealing sleeve is detachably secured to theexterior surface of the tubular body by shear pins.
 9. The apparatus ofclaim 8, wherein one selects the pre-selected pressure threshold atwhich the external sealing sleeve moves by using a greater number orfewer number of shear pins.
 10. The apparatus of claim 8, wherein theexterior surface of the tubular body has a circumferential shear pingroove to accommodate the shear pins.
 11. A method for use inselectively fracing a well, comprising: (a) providing a plurality ofapparatus, each apparatus comprising: a tubular body having an exteriorsurface, and an interior surface that defines an interior bore; anannular flow area having at least one fluid flow port extending radiallythrough the tubular body from the interior surface to the exteriorsurface to permit fluids from the interior bore to pass through the atleast one fluid flow port into a surrounding earth formation; anexternal sealing sleeve detachably secured to the exterior surface ofthe tubular body to selectively cover the annular flow area and closethe at least one fluid flow port; a pressure actuated sleeve shiftingmechanism, where increasing pressure tending to cause axial movement ofthe external sealing sleeve, such axial movement being resisted until apre-selected pressure threshold is reached to permit movement of theexternal sealing sleeve to open the at least one fluid flow port; (b)deploying the apparatuses along a production tubing string in a wellwith packers being positioned between the apparatuses to isolateproduction areas, the pre-selected pressure threshold for eachproduction area increasing from a toe of the well toward a heel of thewell; (c) selectively shifting an external sealing sleeve to an openposition by applying fluid pressure to the pressure actuated sleeveshifting mechanism; (d) continuing to apply fluid pressure to pumpfluids into the earth formation through the apparatus that has had itsexternal sealing sleeve moved to the open position; (e) preventingadditional flow through the apparatus that has had its external sealingsleeve moved to the open position; (f) repeating steps (c), (d), and (e)to selectively open the external sealing sleeve in apparatus in theproduction tubing in stages working toward a wellhead of the well from aremote end of the well.
 12. The method of claim 11, wherein the pressureactuated sleeve shifting mechanism is a fluid cavity formed between theexternal sealing sleeve and the exterior surface of the tubular body,the fluid cavity being asymmetrical to provide an asymmetrical pressuredistribution so that increasing pressure within the fluid cavity tendsto cause axial movement of the external sealing sleeve.
 13. The methodof claim 11, wherein the pressure actuated sleeve shifting mechanism isan inclined plane in fluid pressure communication with at least onefluid flow port.
 14. The method of claim 11, wherein selectivelyshifting the external sealing sleeve to the open position comprisesusing an isolation tool inserted into the tubular body, the isolationtool isolating fluid pressure to a desired portion of the interiorsurface of the tubular body.
 15. The method of claim 11, whereinselectively shifting the external sealing sleve to the open positioncomprises pumping fluids down the production tubing at pressures justsufficient to selectively shift the external sealing sleeve of theapparatus having a lowest shifting pressure to an open position withoutshifting the external sealing sleeve of others of the apparatus havinghigher shifting pressures.
 16. The method of claim 11, whereinpreventing additional flow comprises: pumping balls down the productiontubing until the balls seat on and close the at least one fluid flowport on the apparatus that has had its external sealing sleeve moved tothe open position; and using fluid pressure to maintain the balls seatedon the at least one fluid flow port while other of the external sealingsleeves in the production tubing are selectively moved to the openposition.
 17. In combination: a production tubing string having aplurality of apparatuses for use in selectively fracing a well and anisolation tool, each apparatus for use in selectively fracing a wellcomprising: a tubular body having an exterior surface, and an interiorsurface that defines an interior bore; an annular flow area having atleast one fluid flow port extending radially through the tubular bodyfrom the interior surface to the exterior surface to permit fluids fromthe interior bore to pass through the at least one fluid flow port intoa surrounding earth formation; an external sealing sleeve detachablysecured to the exterior surface of the tubular body to selectively coverthe annular flow area and close the at least one fluid flow port; and apressure actuated sleeve shifting mechanism, where increasing pressuretending to cause axial movement of the external sealing sleeve, suchaxial movement being resisted until a pre-selected pressure threshold isreached to permit movement of the external sealing sleeve to open the atleast one fluid flow port; and an isolation tool at least partiallyextended into the production tubing string, comprising: a tubular bodyhaving a fluid input in fluid communication with a fluid output; sealspositioned on either side of the fluid output, the seals being adaptedto seal against the interior surface of the tubular body such that fluidflowing from the output is isolated to a desired portion of the interiorsurface of the tubular body.
 18. An isolation tool for selectivelyapplying pressure to a pressure actuated opening of an outer tubularbody, the isolation tool comprising: a tubular body carrying a firstsealing element and a second sealing element, the tubular body having afluid inlet and a fluid outlet, the tubular body being movable withinthe outer tubular body; a pressure cavity defined by an outer surface ofthe tubular body, the inner surface of the outer tubular body, and thefirst and second sealing elements, the fluid outlet of the tubular bodybeing in fluid communication with the pressure cavity; the first sealingelement and the second sealing element permitting fluid flow into thepressure cavity and sealing against fluid flow out of the pressurecavity.
 19. The isolation tool of claim 18, further comprising anequalizing valve that is open when the isolation tool is being run intothe outer tubular body and closes upon application of the fluid pressurewithin the pressure cavity.